The present invention relates to a webbing guide for a vehicle safety restraint seat belt. Such a webbing guide is Commonly known as a D-ring and is fixed to a vehicle support pillar behind the seat, approximately at shoulder level, to provide an upper anchorage for, and to guide, the belt webbing as it changes direction from the vertical line coming from the retractor usually fixed at the base of the pillar, to a diagonal line across the occupant""s torso.
Traditional webbing guides comprise a guiding surface in the form of a bar suspended below a hole about which the guide is pivoted on the pillar. Ideally the bar should be set a large distance from the pivot point but this is impractical in the small space available in a vehicle and would make the guides too expensive for practical use.
A common problem with such guides is that the webbing tends to bunch at one end of the bar when it is subject to off-centre loads during a crash, increasing frictional forces between the webbing and the bar and inhibiting the free running of the webbing, leading to excess wear on the belt, and additional crash loading for the vehicle occupant. In extreme cases, the webbing can jam. This is evidently undesirable. Attempts have been made to minimise the problem for example by providing grooves in the surface of the bar. This is expensive and has only shown limited success in alleviating the problem.
It is an object of the invention to provide an improved webbing guide.
A seat belt webbing guide comprising a guide surface in the form of a generally cylindrical bar which has a continuous outer surface over which seat belt webbing passes in use, following an upside-down U-shaped path, there being a top portion to the surface and two side portions, the top portion and at least one side portion are shaped so as to present a contoured surface to the seat belt webbing.
Preferably, the central area of the top portion is raised, and the central area of the at least one of the side portions is recessed.
Alternatively, an opposite contour arrangement could be provided in that the central area of the top portion is recessed and the central area of the at least one side portion may then be raised.
The surface presented to the seat belt webbing may be smooth or may be provided with formations such as being inset with grooves.
Preferably the contour of the surface is such that each warp and weft fibre of the belt webbing contacts the surface for a substantially identical distance, i.e. the surface of the bar presented to the webbing, has a substantially identical sized contour, measured in a circumferential sense around the bar, across the width and along the length of the contact patch of the webbing with the loop.
According to a preferred embodiment of the present invention, each side portion of the surface has its central area recessed.
The raised hump in the central area of the top portion of the surface effectively vectorises the contact forces between the webbing and the surface towards the centre of the surface, providing self-centring for the guide. Additionally the transverse force components thus created augment frictional resistance to sideways movement of the webbing.
The guide of the invention thus has increased resistance to transverse movement of the webbing, thus resisting bunching of the webbing, and also a self-centring property leading to improved stability.
The recessed side portion or portions serve to equalise the contact length of the webbing with the guide over the width of the webbing to avoid higher loads in the centre which would cause excessive wear on the belt and on the guide and possibly lead to failure.